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Helix pomatia:hibernation
When the temperature gets to about 8 degrees Celsius Vineyardsnails get slower and eat
less.They will find protective places,for example where there is cover
of grass,leaves or moss.After about two days they start looking for a good place
where they can build a hole.The snail crawls into the hole and takes a position in
which the shellmouth is turned upwards.The shellmouth is being closed through the
sekretion of slime and a calcium substance.This cover is about a millimeter thick.
Then the animal draws back further into the shell,exhales oxygen and builds 
another cover,this time only with slime.Then a third one is made,so that a number
of airchambers originate.
A snail can survive very cold winters this way,even a temperature of -100 Celsius
is not fatal.The danger lays in high temperature changes.For example when,after
a period of freezing conditions,the temperature goes up,the snails eject
their covers.When it then starts freezing again the snails are not able to 
build another protective cover(epiphragm)and die.
Even though the shell is sealed off doesn't mean the snails metabolism is 
totally stopped.Through the porous epiphragm air is being exchanged.
The heartbeat is reduced to 3-4 beats a minute,compared to 36 in an active

When the temperature gets above 8 degrees celsius the snails becoming active again
and reject their covers.They are very vulnerable during that time,especially
when the temperature drops down suddenly(nightfrosts).This can cause lots
of fatalities.